1. Field of the Invention
This invention relates to metal-working tools and especially to metal-working tools through which electric current is passed for heating a workpiece.
2. Description of the Prior Art
Many metals, such as Inconel 718, titanium, etc., react to being worked by work-hardening, i.e., lose ductility and crack, when they are worked by various techniques, such as forming with dies and punches in a press, drilling with drill bits, turning in a lathe, etc. It has been found that work-hardening can be reduced or eliminated by heating the metallic workpiece. Also, these materials are difficult to machine which results in slow metal-removal rates and short tool life.
One method of heating the workpiece is by resistance heating. An electric current can be passed through the metal-working tool into the workpiece, thereby heating the workpiece at the shear zone. Unfortunately, while heating the shear zone of the workpiece, the cutting edge of the metal-working tool is also heated causing rapid deterioration of the metal-working tool. The tool has to be replaced frequently with extra down-time and expense being added to the metal-working portion of the manufacturing process.